Neuronal death induced by misfolded prion protein is due to NAD+ depletion and can be relieved in vitro and in vivo by NAD+ replenishment

Abstract

The mechanisms of neuronal death in protein misfolding neurodegenerative diseases such as Alzheimer's, Parkinson's and prion diseases are poorly understood. We used a highly toxic misfolded prion protein (TPrP) model to understand neurotoxicity induced by prion protein misfolding. We show that abnormal autophagy activation and neuronal demise is due to severe, neuron-specific, nicotinamide adenine dinucleotide (NAD(+)) depletion. Toxic prion protein-exposed neuronal cells exhibit dramatic reductions of intracellular NAD(+) followed by decreased ATP production, and are completely rescued by treatment with NAD(+) or its precursor nicotinamide because of restoration of physiological NAD(+) levels. Toxic prion protein-induced NAD(+) depletion results from PARP1-independent excessive protein ADP-ribosylations. In vivo, toxic prion protein-induced degeneration of hippocampal neurons is prevented dose-dependently by intracerebral injection of NAD(+). Intranasal NAD(+) treatment of prion-infected sick mice significantly improves activity and delays motor impairment. Our study reveals NAD(+) starvation as a novel mechanism of autophagy activation and neurodegeneration induced by a misfolded amyloidogenic protein. We propose the development of NAD(+) replenishment strategies for neuroprotection in prion diseases and possibly other protein misfolding neurodegenerative diseases.

NAMPT-Mediated NAD+ Biosynthesis Is Essential for Vision In Mice

“…Given these numerous functions, NAD + has been shown to be important in many biological processes, including metabolism (Garten et al, 2009; Mouchiroud et al, 2013), circadian rhythms (Nakahata et al, 2009; Ramsey et al, 2009), and aging (Imai and Guarente, 2014). Relevant to our studies, NAD + has also been shown to be important in neurodegeneration (Alano et al, 2010; Gerdts et al, 2015; Stein et al, 2014; Zhou et al, 2015). However, the role of NAD + in retinal degeneration has been relatively unexplored to date.…”

Temporal Resolution of Misfolded Prion Protein Transport, Accumulation, Glial Activation, and Neuronal Death in the Retinas of Mice Inoculated with Scrapie

“…Similarly, evaluation of an immunomodulatory or neuroprotective compound between 90 and 120 dpi could provide key information about the relationship between activated microglia and neuronal death in prion disease. 4 The results reported herein contribute to a sizable body of work describing the time course of prion disease. A great deal has been done to identify early biomarkers of disease in cattle, 40e42 cervids, 43,44 primates, 45 sheep, 46 and rodent models of TSEs.…”

Prion Infectivity Plateaus and Conversion to Symptomatic Disease Originate from Falling Precursor Levels and Increased Levels of Oligomeric PrP Sc Species

“…A toxic monomeric alpha-helical form of PrP ("TPrP") has been deduced from refolding unglycosylated recombinant PrP and assay upon the PK-1 subline of N2a neuroblastoma cells (27). Toxicity mediated by TPrP was observed in the range of 0.5 to 5 g/ml (27,28), which is in the same general range as PrP C levels measured here in brain homogenates of Prnp ϩ/ϩ and Prnp 0/ϩ mice (i.e., ϳ1.1 and 0.4 g/ml, respectively; Fig. 1).…”

“…A calibration curve was prepared with either recombinant PrP(23-231, 129M) for samples containing full-length PrP Sc or recombinant PrP(90-231, 129M) for samples containing truncated rPrP Sc [PrP (27)(28)(29)(30)] after proteinase K (PK) treatment. The PK-untreated sample containing PrP was divided into a native and a denatured aliquot, where the latter was denatured with 4 M guanidinium HCl for 5 min at 80°C.…”